On the desk in front of me is a set of graphs. The horizontal axis of each represents the years 1750 to 2000. The graphs show, variously, population levels, CO2 concentration in the atmosphere, exploitation of fisheries, destruction of tropical forests, paper consumption, number of motor vehicles, water use, the rate of species extinction and the totality of the human economy's gross domestic product.

What grips me about these graphs (and graphs don't usually grip me) is that though they all show very different things, they have an almost identical shape. A line begins on the left of the page, rising gradually as it moves to the right. Then, in the last inch or so – around 1950 – it veers steeply upwards, like a pilot banking after a cliff has suddenly appeared from what he thought was an empty bank of cloud.

The root cause of all these trends is the same: a rapacious human economy bringing the world swiftly to the brink of chaos. We know this; some of us even attempt to stop it happening. Yet all of these trends continue to get rapidly worse, and there is no sign of that changing soon. What these graphs make clear better than anything else is the cold reality: there is a serious crash on the way.

Yet very few of us are prepared to look honestly at the message this reality is screaming at us: that the civilisation we are a part of is hitting the buffers at full speed, and it is too late to stop it. Instead, most of us – and I include in this generalisation much of the mainstream environmental movement – are still wedded to a vision of the future as an upgraded version of the present. We still believe in "progress", as lazily defined by western liberalism. We still believe that we will be able to continue living more or less the same comfortable lives (albeit with more windfarms and better lightbulbs) if we can only embrace "sustainable development" rapidly enough; and that we can then extend it to the extra 3 billion people who will shortly join us on this already gasping planet.

I think this is simply denial. The writing is on the wall for industrial society, and no amount of ethical shopping or determined protesting is going to change that now. Take a civilisation built on the myth of human exceptionalism and a deeply embedded cultural attitude to "nature"; add a blind belief in technological and material progress; then fuel the whole thing with a power source that is discovered to be disastrously destructive only after we have used it to inflate our numbers and appetites beyond the point of no return. What do you get? We are starting to find out.

We need to get real. Climate change is teetering on the point of no return while our leaders bang the drum for more growth. The economic system we rely upon cannot be tamed without collapsing, for it relies upon that growth to function. And who wants it tamed anyway? Most people in the rich world won't be giving up their cars or holidays without a fight.

Some people – perhaps you – believe that these things should not be said, even if true, because saying them will deprive people of "hope", and without hope there will be no chance of "saving the planet". But false hope is worse than no hope at all. As for saving the planet – what we are really trying to save, as we scrabble around planting turbines on mountains and shouting at ministers, is not the planet but our attachment to the western material culture, which we cannot imagine living without.

The challenge is not how to shore up a crumbling empire with wave machines and global summits, but to start thinking about how we are going to live through its fall, and what we can learn from its collapse.

All the best, Paul

Dear Paul

Like you I have become ever gloomier about our chances of avoiding the crash you predict. For the past few years I have been almost professionally optimistic, exhorting people to keep fighting, knowing that to say there is no hope is to make it so. I still have some faith in our ability to make rational decisions based on evidence. But it is waning.

If it has taken governments this long even to start discussing reform of the common fisheries policy – if they refuse even to make contingency plans for peak oil – what hope is there of working towards a steady-state economy, let alone the voluntary economic contraction ultimately required to avoid either the climate crash or the depletion of crucial resources?

The interesting question, and the one that probably divides us, is this: to what extent should we welcome the likely collapse of industrial civilisation? Or more precisely: to what extent do we believe that some good may come of it?

I detect in your writings, and in the conversations we have had, an attraction towards – almost a yearning for – this apocalypse, a sense that you see it as a cleansing fire that will rid the world of a diseased society. If this is your view, I do not share it. I'm sure we can agree that the immediate consequences of collapse would be hideous: the breakdown of the systems that keep most of us alive; mass starvation; war. These alone surely give us sufficient reason to fight on, however faint our chances appear. But even if we were somehow able to put this out of our minds, I believe that what is likely to come out on the other side will be worse than our current settlement.

Here are three observations: 1 Our species (unlike most of its members) is tough and resilient; 2 When civilisations collapse, psychopaths take over; 3 We seldom learn from others' mistakes.

From the first observation, this follows: even if you are hardened to the fate of humans, you can surely see that our species will not become extinct without causing the extinction of almost all others. However hard we fall, we will recover sufficiently to land another hammer blow on the biosphere. We will continue to do so until there is so little left that even Homo sapiens can no longer survive. This is the ecological destiny of a species possessed of outstanding intelligence, opposable thumbs and an ability to interpret and exploit almost every possible resource – in the absence of political restraint.

From the second and third observations, this follows: instead of gathering as free collectives of happy householders, survivors of this collapse will be subject to the will of people seeking to monopolise remaining resources. This will is likely to be imposed through violence. Political accountability will be a distant memory. The chances of conserving any resource in these circumstances are approximately zero. The human and ecological consequences of the first global collapse are likely to persist for many generations, perhaps for our species' remaining time on earth. To imagine that good could come of the involuntary failure of industrial civilisation is also to succumb to denial. The answer to your question – what will we learn from this collapse? – is nothing.

This is why, despite everything, I fight on. I am not fighting to sustain economic growth. I am fighting to prevent both initial collapse and the repeated catastrophe that follows. However faint the hopes of engineering a soft landing – an ordered and structured downsizing of the global economy – might be, we must keep this possibility alive. Perhaps we are both in denial: I, because I think the fight is still worth having; you, because you think it isn't.

With my best wishes, George

Dear George

You say that you detect in my writing a yearning for apocalypse. I detect in yours a paralysing fear.

You have convinced yourself that there are only two possible futures available to humanity. One we might call Liberal Capitalist Democracy 2.0. Clearly your preferred option, this is much like the world we live in now, only with fossil fuels replaced by solar panels; governments and corporations held to account by active citizens; and growth somehow cast aside in favour of a "steady state economy".

The other we might call McCarthy world, from Cormac McCarthy's novel The Road – which is set in an impossibly hideous post-apocalyptic world, where everything is dead but humans, who are reduced to eating children. Not long ago you suggested in a column that such a future could await us if we didn't continue "the fight".

Your letter continues mining this Hobbesian vein. We have to "fight on" because without modern industrial civilisation the psychopaths will take over, and there will be "mass starvation and war". Leaving aside the fact that psychopaths seem to be running the show already, and millions are suffering today from starvation and war, I think this is a false choice. We both come from a western, Christian culture with a deep apocalyptic tradition. You seem to find it hard to see beyond it. But I am not "yearning" for some archetypal End of Days, because that's not what we face.

We face what John Michael Greer, in his book of the same name, calls a "long descent": a series of ongoing crises brought about by the factors I talked of in my first letter that will bring an end to the all-consuming culture we have imposed upon the Earth. I'm sure "some good will come" from this, for that culture is a weapon of planetary mass destruction.

Our civilisation will not survive in anything like its present form, but we can at least aim for a managed retreat to a saner world. Your alternative – to hold on to nurse for fear of finding something worse – is in any case a century too late. When empires begin to fall, they build their own momentum. But what comes next doesn't have to be McCarthyworld. Fear is a poor guide to the future.

All the best, Paul

Dear Paul

If I have understood you correctly, you are proposing to do nothing to prevent the likely collapse of industrial civilisation. You believe that instead of trying to replace fossil fuels with other energy sources, we should let the system slide. You go on to say that we should not fear this outcome.

How many people do you believe the world could support without either fossil fuels or an equivalent investment in alternative energy? How many would survive without modern industrial civilisation? Two billion? One billion? Under your vision several billion perish. And you tell me we have nothing to fear.

I find it hard to understand how you could be unaffected by this prospect. I accused you of denial before; this looks more like disavowal. I hear a perverse echo in your writing of the philosophies that most offend you: your macho assertion that we have nothing to fear from collapse mirrors the macho assertion that we have nothing to fear from endless growth. Both positions betray a refusal to engage with physical reality.

Your disavowal is informed by a misunderstanding. You maintain that modern industrial civilisation "is a weapon of planetary mass destruction". Anyone apprised of the palaeolithic massacre of the African and Eurasian megafauna, or the extermination of the great beasts of the Americas, or the massive carbon pulse produced by deforestation in the Neolithic must be able to see that the weapon of planetary mass destruction is not the current culture, but humankind.

You would purge the planet of industrial civilisation, at the cost of billions of lives, only to discover that you have not invoked "a saner world" but just another phase of destruction.

Strange as it seems, a de-fanged, steady-state version of the current settlement might offer the best prospect humankind has ever had of avoiding collapse. For the first time in our history we are well-informed about the extent and causes of our ecological crises, know what should be done to avert them, and have the global means – if only the political will were present – of preventing them. Faced with your alternative – sit back and watch billions die – Liberal Democracy 2.0 looks like a pretty good option.

With my best wishes, George

Dear George

Macho, moi? You've been using the word "fight" at a Dick Cheney-like rate. Now my lack of fighting spirit sees me accused of complicity in mass death. This seems a fairly macho accusation.

Perhaps the heart of our disagreement can be found in a single sentence in your last letter: "You are proposing to do nothing to prevent the likely collapse of industrial civilisation." This invites a question: what do you think I could do? What do you think you can do?

You've suggested several times that the hideous death of billions is the only alternative to a retooled status quo. Even if I accepted this loaded claim, which seems designed to make me look like a heartless fascist, it would get us nowhere because a retooled status quo is a fantasy and even you are close to admitting it. Rather than "do nothing" in response, I'd suggest we get some perspective on the root cause of this crisis – not human beings but the cultures within which they operate.

Civilisations live and die by their founding myths. Our myths tell us that humanity is separate from something called "nature", which is a "resource" for our use. They tell us there are no limits to human abilities, and that technology, science and our ineffable wisdom can fix everything. Above all, they tell us that we are in control. This craving for control underpins your approach. If we can just persaude the politicians to do A, B and C swiftly enough, then we will be saved. But what climate change shows us is that we are not in control, either of the biosphere or of the machine which is destroying it. Accepting that fact is our biggest challenge.

I think our task is to negotiate the coming descent as best we can, while creating new myths that put humanity in its proper place. Recently I co-founded a new initiative, the Dark Mountain Project, which aims to help do that. It won't save the world, but it might help us think about how to live through a hard century. You'd be welcome to join us.

Very best, Paul

Dear Paul

Yes, the words I use are fierce, but yours are strangely neutral. I note that you have failed to answer my question about how many people the world could support without modern forms of energy and the systems they sustain, but 2 billion is surely the optimistic extreme. You describe this mass cull as "a long descent" or a "retreat to a saner world". Have you ever considered a job in the Ministry of Defence press office?

I draw the trifling issue of a few billion fatalities to your attention not to make you look like a heartless fascist but because it's a reality with which you refuse to engage. You don't see it because to do so would be to accept the need for action. But of course you aren't doing nothing. You propose to stiffen the sinews, summon up the blood, and, er … "get some perspective on the root cause of this crisis". Fine: we could all do with some perspective. But without action – informed, focused and immediate – the crisis will happen. I agree that the chances of success are small. But they are non-existent if we give up before we have started. You mock this impulse as a "craving for control". I see it as an attempt at survival.

What could you do? You know the answer as well as I do. Join up, protest, propose, create. It's messy, endless and uncertain of success. Perhaps you see yourself as above this futility, but it's all we've got and all we've ever had. And sometimes it works.

The curious outcome of this debate is that while I began as the optimist and you the pessimist, our roles have reversed. You appear to believe that though it is impossible to tame the global economy, it is possible to change our founding myths, some of which predate industrial civilisation by several thousand years. You also believe that good can come of a collapse that deprives most of the population of its means of survival. This strikes me as something more than optimism: a millenarian fantasy, perhaps, of Redemption after the Fall. Perhaps it is the perfect foil to my apocalyptic vision.